This invention relates, generally, to a high density contact and more particularly to an electrical contact which may have a surface coated with tin as opposed to gold, having a very short contact length for use with very high frequency electrical signals in high density applications.
With the advent of VLSI circuitry electrical interconnection scheme between adjacent components and their circuit boards requires more and more dense interwire configurations. Additionally, the circuit path length becomes very critical in order to minimize impedance and resistive effects which may alter circuit performance. Two examples of high density contacts which attempt to minimize contact circuit path length may be found in U.S. Pat. No. 4,354,729 "Preloaded Electrical Contact Terminal" issued Oct. 19, 1982, to Grabbe et al. and U.S. Pat. No. 4,268,102 "Low Impedance Electrical Connecting Means from Spaced-Apart Conductors" issued May 19, 1981 to Grabbe. Coupled with these considerations are the need to provide relatively high contact mating forces. Accordingly, gold is generally utilized to plate some if not all of the contact thereby providing less electrical resistance and therefor allowing for lower mating forces.
It is desirable to have a device which is suitable for high density use such as for VLSI chip carriers which does not require the use of precious metals such as gold. Further, it is also desirable to have a device which is relatively simple as well as inexpensive to manufacture. Additionally, it is desirable to have a contact which is replacable, does not use solder as a means of attachment and which provides a wiping motion during contact mating in order to remove absorbed films and oxides which may be present, thereby establishing good metal to metal contact.
Accordingly, the present invention teaches and as an object of the present invention an electrical contact for high density usage comprising a chip carrier having conductive paths thereon, a circuit board having a conductive strip contained thereon, the housing disposed on the circuit board for receiving electrical contacts therein and the carrier thereon, a contact disposed in the housing, the contact having substantially all of its parts lying in a single plane and having a generally "U"-shaped first portion wherein the legs of the "U"-shape comprise an upper and lower cantilever member, the upper and lower cantilevers having outer and inner beams attached perpendicularly respectively thereto, the outer beam having an upper contact surface disposed at the point wherein the outer beam and the upper cantilever meet and having a lower contact surface at the free end of the outer beam, and an inner beam comprised of a second "U"-shaped member having the first leg as a shunt portion which is perpendicularly attached to the end of the lower cantilever and the second leg defining an inner arm having an inner arm beam contact surface attached at the end thereof, the inner arm being resiliently biased against the lower contact surface of the outer beam, the contact being further characterized in that the inner and outer beams are in overlapping relationship such that vertical movement of the chip carrier on the upper contact surface results in a wiping motion between the lower contact surface and the second leg of the inner beam and between the inner beam contact surface and the conductive strip with a resulting development of a contact mating force whereby current flows from the conductive paths through the upper contact surface, the interface point between the lower contact surface and the inner arm of the inner beam and through the inner beam contact surface to the conductive strip.